1. Field of the Invention
The present invention relates to a vertical external cavity surface emitting laser (VECSEL), and more particularly, to a VECSEL in which a pump laser is integrated with the rest of the VECSEL.
2. Description of the Related Art
Generally, semiconductor lasers are classified into edge emitting lasers in which a light beam is emitted parallel to a substrate and vertical cavity surface emitting lasers (VCSELs) in which a light beam is emitted in a direction perpendicular to a substrate. A VCSEL oscillates in a single longitudinal mode of a very narrow spectrum and emits a beam having a small radiation angle. Also, as integration with other appliances is easy due to the characteristics of surface light emission, the VCSEL can be used as a pumping light source. However, a conventional VCSEL makes single transverse mode oscillation difficult in comparison with the edge emitting lasers. Also, transverse mode operation of the conventional VCSEL requires a small oscillation region. Thus, the output power of the VCSEL is low.
A vertical external cavity surface emitting laser (VECSEL) provides the advantages of a VCSEL described above while realizing high power output at the same time. The VECSEL has an external mirror in place of an upper DBR included in a VCSEL, and thus has a larger gain area and can obtain an output power of several to several tens of watts or more.
FIG. 1 is a schematic cross-sectional view of a VECSEL 10 using conventional optical pumping. Referring to FIG. 1, the conventional VECSEL 10 includes a heat sink 11, a Distributed Bragg Reflector (DBR) layer 12 formed on the heat sink 11, an active layer 13, an external mirror 14 separated from the active layer 13 by a predetermined distance, and a pump laser 16 exciting the active layer 13. A second harmonic generation (SHG) crystal 15 doubles the frequency of light between the active layer 13 and the external mirror 14. The active layer 13 may have a multiple quantum well structure having a resonant periodic gain (RPG) structure, and emits light with a predetermined wavelength. The heat sink 11 exhausts heat generated in the active layer 13 to cool the active layer 13. A resonant cavity is formed between the DBR layer 12 and the concave external mirror 14. The pump laser 16 emits light at a shorter wavelength than the wavelength of the light generated by the active layer 13. The light from the pump laser 16 passes through a lens array 17 onto the active layer 13 to excite the active layer 13.
In the above described structure, when the light at a relatively short wavelength generated by the pump laser 16 is incident on the active layer 13 through the lens array 17, the active layer 13 is excited and emits light with a predetermined wavelength. The light is repeatedly reflected between the DBR layer 12 in the lower portion of the active layer 13 and the external mirror 14 to reciprocate through the active layer 13. Thus a portion of the light amplified in the active layer 13 is output to the outside as a laser beam through the external mirror 14 and the rest of the light is reflected again to be used for optical pumping in the active layer 13.
However, the active layer 13 and the pump laser 16 are manufactured separately and then integrated in the VECSEL 10. Additionally, the pump laser 16 should be oriented at a proper angle such that the light emitted from the pump laser 16 can be incident on the active layer 13, and a lens array 17 should be disposed between the pump laser 16 and the active layer 13. Accordingly, mass production of the laser device is difficult and the size of the laser increases. Thus the manufacturing time and costs are increased.